Adaptive compensation of MOSFET-C filters

At high frequencies MOSFET-C filters suffer from Q-enhancement due to phase lag introduced by the finite gain-bandwidth of operational amplifiers. Several compensation schemes, which can be classified as either passive or active schemes, have been proposed for cancelling this phase lag. The passive schemes are simple to implement, but the compensation of phase lag takes place only at a certain frequency. On the other hand the active schemes which have excellent tracking characteristics require more power and area for their implementation. We introduce a new adaptive compensation scheme which combines the simplicity of the passive schemes with the effectiveness of the active schemes. First the theory is developed and then results of simulations as well as the actual testing of an adaptively compensated universal filter are presented